Conventionally, quinazolin-4-one derivatives are prepared, for example by the process disclosed in J. Org. Chem., 41 (10), 1763 (1976) which comprises heating a diamide derivative for cyclization. However, since the process employs a high heating temperature (250.degree. C. or above), it produces the quinazolin-4-one derivative in a very low yield and generates large amounts of byproducts.
An object of the present invention is to provide a novel process for preparing a series of quinazolin-4-one derivatives useful as pharmaceuticals or intermediates for synthesis thereof in higher yields with reduced amounts of byproducts.
The present inventors carried out extensive research and found that the following process can achieve the above object. The present invention has been accomplished based on the finding.